U.S. patent application number 11/976916 was filed with the patent office on 2010-08-26 for method for making multi-cystalline film of solar cell.
This patent application is currently assigned to ATOMIC ENERGY COUNCIL - INSTITUTE OF NUCLEAR ENERGY RESEARCH. Invention is credited to Chin-Chen Chiang, Yu-Hsiang Huang, Chien-Te Ku, Shan-Ming Lan, Wei-Yang Ma, Tsun-Neng Yang.
Application Number | 20100216278 11/976916 |
Document ID | / |
Family ID | 42631337 |
Filed Date | 2010-08-26 |
United States Patent
Application |
20100216278 |
Kind Code |
A1 |
Yang; Tsun-Neng ; et
al. |
August 26, 2010 |
Method for making multi-cystalline film of solar cell
Abstract
A method is disclosed for making a multi-crystalline silicon
film of a solar cell. In the method, a titanium-based film is
coated on a ceramic substrate. A back surface field layer is coated
on the titanium-based film via providing dichlorosilane and
diborane in an atmospheric pressure chemical vapor deposition
process at a first temperature. A light-soaking layer is coated on
the back surface field layer via providing more dichlorosilane and
diborane in the atmospheric pressure chemical vapor deposition
process at a second temperature higher than the first
temperature.
Inventors: |
Yang; Tsun-Neng; (Taipei
City, TW) ; Lan; Shan-Ming; (Taoyuan County, TW)
; Chiang; Chin-Chen; (Taoyuan County, TW) ; Ma;
Wei-Yang; (Banqiao City, TW) ; Ku; Chien-Te;
(Pingzhen City, TW) ; Huang; Yu-Hsiang; (Pingzhen
City, TW) |
Correspondence
Address: |
Jackson Intellectual Property Group PLLC
106 Starvale Lane
Shipman
VA
22971
US
|
Assignee: |
ATOMIC ENERGY COUNCIL - INSTITUTE
OF NUCLEAR ENERGY RESEARCH
Taoyuan
TW
|
Family ID: |
42631337 |
Appl. No.: |
11/976916 |
Filed: |
October 29, 2007 |
Current U.S.
Class: |
438/97 ;
257/E21.09 |
Current CPC
Class: |
Y02P 70/521 20151101;
H01L 31/182 20130101; H01L 31/022425 20130101; Y02E 10/546
20130101; Y02P 70/50 20151101; C23C 16/24 20130101; H01L 31/03921
20130101 |
Class at
Publication: |
438/97 ;
257/E21.09 |
International
Class: |
H01L 21/20 20060101
H01L021/20 |
Claims
1. A method for making a multi-crystalline silicon film of a solar
cell, the method comprising the steps of: providing a ceramic
substrate; coating a titanium-based film on the ceramic substrate;
coating a back surface field layer on the titanium-based film via
providing dichlorosilane and diborane in an atmospheric pressure
chemical vapor deposition process at a first temperature; and
coating a light-soaking layer on the back surface field layer via
providing dichlorosilane and diborane in the atmospheric pressure
chemical vapor deposition process at a second temperature higher
than the first temperature.
2. The method according to claim 1, wherein the thickness of the
ceramic substrate is about 0.1 to 1.0 mm.
3. The method according to claim 1, wherein the titanium-based film
is made of a material selected from a group consisting of
TiSi.sub.2, TiN, TiC, TiB.sub.2 and TiC.sub.xN.sub.y.
4. The method according to claim 1, wherein the thickness of the
titanium-based film is about 1000 to 5000 angstroms.
5. The method according to claim 1, wherein the titanium-based film
is used both as a back contact and a seed layer.
6. The method according to claim 1, wherein the first temperature
is about 900 to 1000 degrees Celsius.
7. The method according to claim 1, wherein the rate of the
epitaxial growth rate of the light-soaking layer is higher than
about 0.5 micrometer/minute.
8. The method according to claim 1, wherein the thickness of the
light-soaking layer is about 1 to 15 micrometers.
9. The method according to claim 1, wherein the size of silicon
crystals in the light-soaking layer is larger than 10 micrometers.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to a solar cell and, more
particularly, to a method for making a multi-crystalline silicon
film in a solar cell.
[0003] 2. Related Prior Art
[0004] Most silicon-based solar cells are made in low-temperature
processes based on plasma-enhanced chemical vapor deposition
("PECVD"). An amorphous silicon or multi-crystalline silicon film
is coated on a glass, aluminum, silicon, stainless steel or plastic
substrate. A back contact is made of aluminum, gold, silver or
transparent conductive oxide such as indium-tin oxide ("ITO") and
zinc oxide.
[0005] The primary advantage of the low-temperature processes is
the wide variety of materials that can be used to make the
substrates. However, they suffer drawbacks such as defective
silicon films, low photoelectrical conversion efficiencies and low
light-soaking stability.
[0006] In the PECVD, while coating the microcrystalline silicon
film, a silicon material is highly diluted in hydrogen. For
example, [H.sub.2]/[SiH.sub.4]>15. That is, the concentration or
flow rate of H.sub.2 is more than 15 times as high as that of
SiH.sub.4. The problems with the PECVD are a low growth rate of the
film, a long process and a high cost.
[0007] Regarding the making of the poly-silicon solar cells, there
are various techniques such as solid phase crystallization ("SPC")
and aluminum-induced crystallization ("AIC"). The SPC is based on
the PECVD. An amorphous silicon film is deposited, intensively
heated and annealed at a high temperature. Thus, a poly-silicon
film with a grain size of 1 to 2 micrometers is made.
[0008] In the AIC as shown in FIGS. 5 through 9, an aluminum film
32 is coated on a substrate 31. An amorphous silicon film 33 is
coated on the aluminum film 32 based on the PECVD and annealed at a
temperature of about 575 degrees Celsius for a long time to form a
seeding layer 34. Then, it is subjected to an epitaxial process
such as the PECVD or an electron cyclotron resonance chemical
deposition ("ECR-CVD") to make a poly-silicon film 35. The AIC
however involves many steps and takes a long time. The resultant
grain size is about 0.1 to 10 micrometers.
[0009] As discussed above, regarding the conventional methods for
making poly-silicon film solar cells in the low-temperature
processes based on the PECVD, there are many defects in the silicon
films, the photoelectrical conversion efficiencies are low, the
light soaking stabilities low, the growth rates of the films low,
the processes long, and the costs high. Concerning the method for
making poly-silicon film solar cells based on the AIC, the
processes are long for including many steps and therefore
expensive.
[0010] The present invention is therefore intended to obviate or at
least alleviate the problems encountered in prior art.
SUMMARY OF INVENTION
[0011] It is an objective of the present invention is to provide an
efficient method for making a multi-crystalline silicon film of a
solar cell.
[0012] It is another objective of the present invention to provide
a method for providing a quality multi-crystalline silicon film of
a solar cell.
[0013] It is another objective of the present invention to provide
a method for making a multi-crystalline silicon film that can be
used to make a solar cell that exhibits a high photoelectrical
conversion efficiency and stable light-soaking.
[0014] To achieve the fore-going objectives, in a method, a
titanium-based film is coated on a ceramic substrate. A back
surface field layer is coated on the titanium-based film via
providing dichlorosilane and diborane in an atmospheric pressure
chemical vapor deposition process at a first temperature. A
light-soaking layer is coated on the back surface field layer via
providing more dichlorosilane and diborane in the atmospheric
pressure chemical vapor deposition process at a second temperature
higher than the first temperature.
[0015] Other objectives, advantages and features of the present
invention will become apparent from the following description
referring to the attached drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0016] The present invention will be described via detailed
illustration of the preferred embodiment referring to the
drawings.
[0017] FIG. 1 is a flowchart of a method for making a
multi-crystalline silicon film of a solar cell according to the
preferred embodiment of the present invention.
[0018] FIG. 2 is a side view of a ceramic substrate coated with a
back contact in the method shown in FIG. 1.
[0019] FIG. 3 is a side view of a back surface field layer coated
on the back contact shown in FIG. 2.
[0020] FIG. 4 is a side view of a light-soaking layer coated on the
back surface field layer shown in FIG. 3.
[0021] FIG. 5 is a side view of a substrate used in a conventional
method for making a multi-crystalline silicon film.
[0022] FIG. 6 is a side view of an aluminum film coated on the
substrate shown in FIG. 5.
[0023] FIG. 7 is a side view of an amorphous silicon film coated on
the aluminum film shown in FIG. 6.
[0024] FIG. 8 is a side view of the substrate coated with a seed
layer converted from the amorphous silicon film and the aluminum
film shown in FIG. 7.
[0025] FIG. 9 is a side view of a multi-crystalline silicon film
coated on the seed layer shown in FIG. 6.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0026] Referring to FIG. 1, shown is a method for making a
multi-crystalline silicon film of a solar cell according to the
preferred embodiment of the present invention.
[0027] Referring to FIGS. 1 and 2, at 11, a ceramic substrate 21 is
provided. The ceramic substrate 21 is made of aluminum oxide. The
thickness of the substrate 21 is about 0.1 to 1.0 mm. A
titanium-based film 22 is coated on the ceramic substrate 21. The
thickness of the titanium-based film 22 is about 1000 to 5000
angstroms. The titanium-based film 22 is used both as a back
contact and a seed layer. The titanium-based film 22 is made of
TiSi.sub.2, TiN, TiC, TiB.sub.2 or TiC.sub.xN.sub.y.
[0028] Referring to FIGS. 1 and 3, at 12, in an atmospheric
pressure chemical vapor deposition ("APCVD") device, at about 900
to 1000 degrees Celsius, for about 5 minutes, dichlorosilane and
diborane exchange silicon atoms and boron atoms, thus causing the
epitaxial growth of a back surface field ("BSF") layer 23 on the
titanium-based film 22. This exchange is called "inter-doping." The
concentration of the boron atoms in the BSF layer 23 is about
10.sup.18 #/mm.sup.3.
[0029] Referring to FIGS. 1 and 4, at 13, at higher than 1000
degrees Celsius, for about 30 minutes, the dichlorosilane and the
diborane exchange silicon atoms and boron atoms, thus causing the
epitaxial growth of a light-soaking layer 24 on the BSF layer 23,
which is used as a core layer. The rate of the epitaxial growth is
about 0.5 micrometer/minute. The thickness of the light-soaking
layer 24 is about 1 to 15 micrometers. The size of silicon crystals
241 in the light-soaking layer 24 is about 10 micrometers. The
concentration of the boron atoms in the light-soaking layer 24 is
about 10.sup.16 to 10.sup.17 #/mm.sup.3.
[0030] As discussed above, the atmospheric pressure chemical vapor
deposition process is conducted at higher than 900 degrees Celsius.
The ceramic substrate 21 is made of aluminum oxide. The
titanium-based layer 22 is used both as the back contact and the
seed layer. Therefore, the rate of the epitaxial growth of the
multi-crystalline silicon film is higher than 0.5
micrometer/minute, and the size of the silicon crystals is larger
than 10 micrometers. Moreover, as multi-crystalline silicon
exhibits high electron-hole mobility, large electron-hole diffusion
length and long electron-hole recombination, the solar cell made
according to the present invention exhibits a high epitaxial growth
rate, excellent crystal quality, a high photoelectrical conversion
efficiency and stable light-soaking. In addition, the cost of
equipment is low, and the process simple.
[0031] The present invention has been described via the detailed
illustration of the preferred embodiment. Those skilled in the art
can derive variations from the preferred embodiment without
departing from the scope of the present invention. Therefore, the
preferred embodiment shall not limit the scope of the present
invention defined in the claims.
* * * * *